CL 216401 introduced a new static array of uint64s running from 0 to 255.

Two follow-ups here:

• We should use it in the compiler instead of staticbytes for byte-sized values (see https://go-review.googlesource.com/c/go/+/216401/2/src/runtime/iface.go#531).

• We should use it in the compiler for larger-sized ints whose value is a constant between 0 and 255.